Method of controlling reverse link transmission

ABSTRACT

The method of controlling reverse link transmission by at least one mobile station includes first scheduling a transmission by at least one mobile station by sending a schedule grant message according to a first scheduling protocol. The schedule grant message provides the mobile station with approval to transmit, and further establishes a rate limit for transmissions scheduled according to a second scheduling protocol.

BACKGROUND OF THE INVENTION

Development of the releases of the CDMA2000 family of standards, as wellas UMTS and other 3^(rd) generation wireless standards, has focused inpart on enhancing the reverse link (mobile station to base station)operation to support high-speed packet data applications. For example,as part of the development of 1xEV-DV Release D, a number of frameworkproposals to enhance the performance of the reverse link are underconsideration. These proposals envision using two types of modes ormethods for scheduling transmissions by the mobile station: a scheduledtransmission mode and a rate control scheduling mode.

The first type, referred to as a scheduled transmission mode, schedulestransmissions by having the base station send a schedule grant messagewith an explicit instruction for the mobile station to transmit. A grantfor a scheduled transmission designates the mobile station that is totransmit as well as the transmission format (data rate, frame/packetduration, and transmission power) the mobile station is to employ. Therate of a transmission is the number of information bits that constitutethe transmission divided by the time interval over which the bits aresent.

The rate control scheduling mode on the other hand provides a looserform of control on mobile station transmissions. Here, the base stationsends a rate control directive or instruction, which is typically a onebit transmission, that can be either broadcast to all mobiles in thecell/sector (common rate control) or transmitted individually to mobilestations (dedicated rate control). The rate control bit has a predefinedmeaning. For example, according to one proposal the rate control bitindicates whether the mobile station is to transmit at a predeterminedrate limit or not transmit at all. The non-zero rate limit is signaledvia an actual transmission to the mobile while the zero rate limit issignaled by the base station transmitter's silence. Such a rate controlmechanism is termed on-off keying. According to another proposal, therate control bit indicates whether the mobile station is to transmit atan increased or decreased rate limit. As a further example, such as whenthe rate control method is being used to affect multiple mobilestations, the rate control bit(s) probabilistically influences the ratelimit.

As will be appreciated from the above discussion, the proposals to dateenvision mutually exclusively using the rate control scheduling mode orthe scheduling transmission mode. For example, according to oneproposal, the scheduling transmission mode is used with mobile stationsthat are not involved in a soft hand-off (a mobile is said to be in softhandoff if it is in simultaneous communication with at least two basestations that are not collocated), and the rate control scheduling modeis used with mobile stations involved in a soft hand-off.

SUMMARY OF THE INVENTION

The present invention provides a method of controlling reverse linktransmissions that permits concurrently operating in both the scheduledtransmission mode and the rate control scheduling mode. According to thepresent invention, the two modes have a cooperative functionalrelationship that reduces the transmission power and/or bandwidth neededon the forward link to schedule mobile transmissions. In many cases, areduced amount of information may be sent on the forward link in orderto schedule a mobile's transmissions.

According to one embodiment, the scheduled transmission mode is used toschedule a transmission and set a rate limit from which the rate controlscheduling mode operates. Namely, a mobile station interprets a ratecontrol bit with respect to the rate limit set by the last schedulegrant message received. In an alternative embodiment the mobile stationtransmits, in response to a rate control instruction, based on a rate ofa previous transmission made by the mobile station in response to aprevious schedule grant message.

According to another embodiment, the schedule grant message overrides acommon rate control instruction. In this embodiment, the available loadat the base station is used to determine whether to send one or moremobile stations respective schedule grant messages, which override thecommon rate control instruction for these mobile stations.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only, wherein like referencenumerals designate corresponding parts in the various drawings, andwherein:

FIG. 1 illustrates communication between the mobile station and the basestation in which a first embodiment of the present invention is employedto schedule transmission;

FIG. 2 illustrates the operational process performed at the mobilestation according to a first embodiment of the present invention;

FIG. 3 illustrates the operational process performed at the base stationaccording to a first embodiment of the present invention;

FIG. 4 illustrates the operational process performed at the mobilestation according to a second embodiment of the present invention; and

FIGS. 5A-5B illustrate the operational process performed at the basestation according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The following description may be described as based on a wirelesscommunication system operating in accordance with the cdma2000 1xEV-DVstandard. Although the exemplary embodiments of the present inventionwill be described in this exemplary context, it should be noted that theexemplary embodiments shown and described herein are meant to beillustrative only and are not limiting in any way. As such, variousmodifications will be apparent to those skilled in the art forapplication to other communications systems, such as the UniversalMobile Telecommunications System (UMTS) as reflected in the high-speeduplink packet access (HSUPA) system specification, for example, and arecontemplated by the teachings herein.

Where used below, a mobile station (or mobile) is a device providingdata connectivity to a user. A mobile station may be connected to acomputing device such as a laptop, personal computer (PC), or it may bea self-contained data device such as a personal digital assistant (PDA)or cellular phone. Accordingly, a mobile station is equivalent to, andmay also be referred to as, an access terminal, wireless mobile, remotestation, user, user equipment (UE), subscriber or any other remote userof wireless resources in a wireless communications network. Further, amobile station may be functionally divided into a computing device suchas a PC, which is responsible for point-to-point protocol (PPP) andhigher later protocol functionality (IP, TCP, RTP, HTTP, etc.) and anaccess terminal (AT). The AT is responsible for the airlink and radiolink protocol (RLP) layers.

Additionally as used herein, a base station refers to network equipmentproviding data connectivity between a packet data network (e.g., theInternet) and one or more mobile stations. A base station may beequivalent to, and may also be referred to as a base transmitterstation, Node-B, access network or radio access network (RAN). An accessnetwork or RAN may be composed of one or more base stations.

Unification of the Control Mechanism for Scheduling and Dedicated RateControl

A first embodiment of the present invention provides a method ofcontrolling reverse link (mobile station to base station) transmissionsthat cooperatively unifies the scheduled transmission mode and dedicatedrate control scheduling mode transmission mechanisms or methods.According to the present invention, the rate limit set by a schedulegrant message in the scheduled transmission mode has a dualfunction/interpretation. The schedule grant serves not only to direct amobile station to transmit at a specified rate (and for a certainduration) in the well-known manner, but also sets or resets the ratelimit for subsequent transmissions scheduled for the mobile stationaccording to the dedicated rate control scheduling method. Thus, theschedule grant message provides both a rate assignment for theparticular transmission as well as a rate limit for later rate controlscheduling method transmissions.

According to one embodiment of the present invention, a base stationsends schedule grant messages over a forward link uplink schedulingchannel (F-USCH), also known as the forward grant channel. Instructions,such as the rate control bit, sent according to the rate controlscheduling mode are sent by the base station over a different channel.More particularly, these instructions are sent on a sub-channel of theforward link control and acknowledgement channel (F-UCACH), alsoreferred to as the rate control channel.

An example operation of the first embodiment of the present inventionwill be described with respect to FIG. 1. Subsequently, the operationalprocess at the mobile station will be described with respect to FIG. 2,and then the operational process at the base station will be describedwith respect to FIG. 3.

FIG. 1 illustrates communication between the mobile station and the basestation in which the method of the present invention is employed toschedule transmissions. FIG. 1 illustrates a first time-line 10 oftransmission performed by the mobile station, a second time-line 12 oftransmission performed by the base station, and a third time-line 14 oftransmission performed by the mobile station.

As shown, particularly with respect to the first time-line 10, when themobile station has data to send to the base station, the mobile stationenters the scheduled transmission mode and transmits asynchronously overthe reverse link packet data control channel (R-PDCCH). The transmissionnotifies the base station that the mobile station has data to transmit.More particularly, the transmission notifies the base station that thedata buffer in the mobile station is not empty, referred to as anon-zero buffer status. In this transmission, the mobile station alsomakes a first pilot report. A pilot report indicates the signal strength(such as the transmitted power) of a primary pilot signal transmitted bythe mobile station to the base station. This signal is referred to asthe R-PPICH (Reverse Link Primary Pilot Channel).

As shown by the first time-line 10, the mobile station will continueperiodically transmitting pilot reports, and only interrupts thetransmission of a pilot report to perform a packet data transmission. Asshown by the second time-line 12, the base station decodes the R-PDCCHand updates information maintained on the mobile station. For example,the base station will update information on the buffer status of themobile station. As a result of this update, in a well-known manner, thebase station schedules transmission by the mobile station by sending aschedule grant message on the F-USCH. As is well known, the schedulegrant message identifies the mobile station and contains information onthe format (rate, duration, and transmission power), and strength withwhich an additional pilot is to be transmitted. This additional pilot,also termed a secondary pilot (R-SPCIH) provides additional data forestimating the channel at the time of data transmission. According tothe present invention, the rate given in the format of the scheduledtransmission will serve the dual role of the rate limit for subsequentmobile station transmissions scheduled according to the rate controlscheduling method.

An alternative embodiment would use the rate at which the mobiletransmits in response to the schedule grant as the reference rate limit.In some cases, it is possible for the mobile to make a transmission at arate that is lower than the granted data due to the smaller number ofbits and/or reduced power available for the transmission.

In response to the schedule grant message, as shown by the thirdtime-line 14, the mobile station transmits reverse link secondary pilotchannel (R-SPICH) and R-PDCCH frames and a corresponding reverse linkpacket data channel (R-PDCH) frame. As is well-known, the R-PDCCHcarries the control and format information for the data beingtransmitted by the mobile station over the R-PDCH. As is furtherwell-known, the R-SPICH is a secondary pilot channel sent by the mobilestation. However, according to the present invention, the mobile stationsets the power at which the secondary pilot channel is transmitted basedon the rate indicated in the schedule grant message. Specifically, themobile station includes a look-up table mapping rate to secondary pilotchannel powers.

The base station receives and decodes the mobile station transmissionand sends acknowledgement (ACK) or negative-acknowledgement (NACK)feedback to the mobile station. An ACK indicates that the transmissionwas received and decoded successfully. A NACK indicates that thetransmission was not properly received and/or decoded. As is well-known,in response to a NACK, the mobile station will attempt are-transmission. In this descriptions re-transmissions are asynchronous,i.e. the re-transmission may follow an arbitrary time after thetransmission, and the base station will indicate to the mobile when itshould make the retransmission.

The mobile station continues to send pilot reports to the base stationas shown in the first time-line 10. The base station may scheduleanother transmission by the mobile station by either sending a schedulegrant message or by utilizing the rate control scheduling method. Aswill be appreciated, and as described in greater detail below, inaccordance with the principals of this embodiment of the presentinvention, the mobile station will monitor both the F-USCH and theF-UCACH.

As will further be appreciated, scheduling in the rate controlscheduling mode is much simpler and requires fewer resources (e.g.,power, bandwidth, duration of the channel is used) to schedule atransmission. FIG. 1 illustrates that the subsequent scheduling of themobile station is performed according to the rate control schedulingmethod. As shown in the second time-line 12, the base station sends asingle-bit rate control instruction. In one embodiment of the presentinvention, the mobile station operates according to the on-off keyingtechnique. Accordingly, when the rate control bit is set/transmitted (asopposed to silence), the mobile station interprets the rate controlinstruction as scheduling a transmission with a rate limit as set in thepreviously received schedule grant message.

The present invention, however, is not limited to this embodiment ofrate control scheduling. Instead, the rate control bit or bits mayindicate whether the mobile station is to transmit at an increased ordecreased rate limit with respect to the rate limit set in thepreviously received schedule grant message. Thus the scheme would usethe rate control bits to increase or decrease the rate limit withrespect to the rate limit set in the previously received schedule grantif the previous transmission is made in response to the schedule grant,or with respect to the previous rate limit if the previous transmissionis made in response to the rate control bit. Also, the adjustments tothe rate limit set by the previously received schedule grant can becumulative so that all rate control bits received between the currenttransmission instant and the previously received schedule grant are usedto determine the current rate limit. Alternatively, the rate controlbits may indicate an increase or decrease with respect to the rate ofthe mobile station's last transmission, and the adjustments to the ratelimit, due to successive rate control bits may accumulate. As a furtherexample, the rate control bit or bits may be used to probabilisticallyinfluence the rate limit set in the previously received schedule grantmessage if the previous transmission is made in response to the schedulegrant, or probabilistically influence the previous rate limit if theprevious transmission is made in response to the rate control bit(s).The rate control bit(s) may also indicate a change (or no change) withrespect to the rate with which the mobile station made its transmissionin response to the schedule grant.

If the mobile station still has data in its buffer, then in response tothe rate control instruction, the mobile station transmits R-SPICH andR-PDCCH frames and a corresponding reverse link packet data channel(R-PDCH) frame in the same manner described previously. If thistransmission will empty the buffer of the mobile station, the mobilestation indicates a zero buffer status in the R-PCCH frame.

Assuming the transmission by the mobile station is received and decoded,the base station, besides acknowledging the transmission, sends arelease message for the mobile station over the F-USCH in response tothe indicated zero buffer status. In response to the release message,the mobile station will halt the periodic sending of the pilot updates.

As discussed above, the base station may schedule subsequenttransmissions according to either the rate control scheduling method orthe scheduled transmission method. If the scheduled transmission methodis reused, then the schedule grant message sent will serve to reset therate limit upon which the rate control scheduling method is based.Furthermore, while an asynchronous operation of rate control schedulingwas described above and will be described in further detail below,performing scheduling according to the principals of the presentinvention for synchronous rate control scheduling will be readilyapparent from the proceeding and following disclosure.

Next, the operational process at the mobile station will be describedwith respect to FIG. 2. As shown, after the mobile station sends theinitial buffer status and the pilot report to enter the scheduling mode,the mobile station monitors the F-USCH and attempts to decode the F-USCHevery scheduling interval in step S20. Then, in step S22, the mobilestation determines if the decoded schedule grant message is for itself.If so, then in step S24 the mobile station performs a transmissionaccording to the transmission format (rate, duration, etc.) set in theschedule grant message, and will set the rate limit as that indicated bythe schedule grant message.

If in step S22 the mobile station does not determine that a schedulegrant message is intended for itself, then in step S26, the mobilestation monitors the F-UCACH for a rate control instruction. If a ratecontrol instruction is sent during the scheduling interval, then themobile station uses the rate limit from the previous schedule grantmessage as the rate limit for performing a transmission according to therate control scheduling method. Alternatively, the rate controlscheduling method employed may, for example, be any of theabove-discussed embodiments. For instance, the rate control could beperformed with respect to the previous rate limit if the previoustransmission is made in response to the rate control bit, and/or theadjustments to the rate limit set by the previously received schedulegrant can be cumulative so that all rate control bits received betweenthe current transmission instant and the previously received schedulegrant are used to determine the current rate limit. If no rate controlinstruction is received in step S26, then processing returns to stepS20. Processing also returns to step S20 after steps S24 and S28.

While the operational process has been described for asynchronous ratecontrol scheduling, it will be appreciated from the previous andfollowing disclosure that synchronous rate control scheduling could beperformed. For example, the second embodiment of the present inventiondescribed in detail below will discuss a synchronous rate controloperation that is readily applicable to this embodiment of the presentinvention. For instance, step S46, S48 and S50 of FIG. 4 may be addedbetween steps S22 and S26 of the present invention to obtain asynchronous rate control operation.

Next, the operational process at the base station will be described withrespect to FIG. 3. As shown, the base station uses any well-known methodto prioritize the scheduling of transmissions by mobile stations, anddetermines in step S30 if the priority established for the mobilestation permits scheduling of transmission by the mobile station. Oncethe priority of the mobile station permits scheduling transmission, thebase station determines in any well known manner the optimumtransmission format (rate, duration and power) for the mobile stationtransmission in step S32.

Then, in step S34, the base station determines if an absolute value ofthe currently determined rate minus the previous rate (i.e., rate limit)assigned to the mobile station is greater than a predeterminedthreshold. Namely, the base station determines if the change in assignedrate limit exceeds a threshold amount. If so, then the base stationschedules transmission of the mobile station according to the scheduledtransmission mode by sending a scheduling grant message over the F-USCHin step S36. If the change in assigned rate limit does not exceed thethreshold amount, then the base station schedules transmission of themobile station according to the rate control scheduling method bysending a rate control instruction in step S38.

The previously described base station procedure shows how a decision ismade to send a rate control command versus a schedule grant to a userthat has been deemed high priority and required to transmit data. Thedescription was in the context of a system that combined scheduling withdedicated on-off rate control with asynchronous operation. The basestation procedures may also include procedures for determining thecontrol messages to be sent to all the users taking into account themaximum load at the base station as well as the currently assigned ratelimits. The maximum load is a measure of the received power that thebase station can tolerate for normal operation of the reverse link forall mobiles in the cell. The maximum load and current rate limits aremetrics that would determine the pools of users to be scheduled versusrate controlled, the actual rate limits for all users, and the controlmessage (schedule grant or rate control command) to be sent to theusers. The next embodiment of the present invention will describe basestation procedures for determining the control messages to be sent toall the users taking into account the maximum load at the base stationas well as the currently assigned rate limits. This procedure isdescribed with respect to FIGS. 5A and 5B and is readily applicable tothe above described embodiment of the present invention. For example,the above-described embodiment of the present invention may adopt theprocedures of FIGS. 5A and 5B, except that steps S68-S72 would bereplaced with the steps of (i) prioritizing the rate control mobilesbased on channel conditions, transmit power headroom, data in theirrespective buffers, etc. in the any well-known manner; and (ii)determine individual rat control bit(s) based on the mobile priority andthe available load at the base station. Namely, in step (ii) the highestpriority mobiles are considered first, and if the available load permitsrate control scheduling of the mobile, then the mobile is ratecontrolled schedule; otherwise, the mobile is not scheduled.

Unification of the Control Mechanism for Scheduling and Common RateControl

A common rate control or scheduling mechanism is one where the datatransmissions of a number of mobile stations are scheduled or controlledby a single or common set of rate control bits. One example of commonrate control is the HRPD (high rate packet data) system based on theIS-856 standard. In this system, the rate control bits known as reverseactivity bits (RAB) are broadcast to all mobile stations in a sector.The received RAB bits (indicating to adjust power up or down) are usedby the mobile stations to ramp up or ramp down their data transmissionrates with pre-determined transition probabilities. The data rates usedby the mobile stations typically move up and down in tandem within asmall band of data rates. Common rate control is also underconsideration for the enhanced reverse link of 1xEV-DV Revision D(IS-2000-D).

A weakness of a common rate control scheme is its inability to givepriority to individual mobile station's data transmissions. Low-latency,high data transmissions by a single (or small number of) mobilestation(s) is often desirable in order to meet quality of service (QoS)requirements.

According to a second embodiment of the present invention, the controlmechanisms for scheduled transmission and common rate control schedulingare integrated by using a schedule grant message to override the ratelimit implied by the sequence of common rate control bits received bythe mobiles.

For the purposes of example only, the second embodiment of the presentinvention will be described using the common rate control schedulingscheme of HRPD as an exemplary common rate control scheduling scheme,but it will be recognized that the present invention is not limited tothis common rate control scheduling scheme.

The second embodiment of the present invention will also be described inthe context of a system with synchronous acknowledgements andretransmissions. An acknowledgement is said to be synchronous if thereexists a fixed timing relationship between transmission of a data packetand the acknowledgement of its successful or unsuccessful receipt at thereceiver. Similarly synchronous retransmissions occur a fixed timeinterval after unsuccessful reception of a data transmission.

The use of the control mechanism described here may be extended in astraightforward manner to the cases where either the acknowledgements,retransmissions, or both are asynchronous, i.e. do not maintain a fixedtiming relationship with the initial data transmission.

Examples of the mobile station and base station procedures to be usedwhen a schedule granting mechanism is integrated in a system with commonrate control scheduling will be described with respect to FIGS. 4 and5A-5B, respectively.

FIG. 4 illustrates the operational process performed at the mobilestation according to a second embodiment of the present invention. Asshown, the mobile station monitors the F-USCH and attempts to decode theF-USCH every scheduling interval in step S40. Then, in step S42, themobile station determines if the decoded schedule grant message is foritself. If so, then in step S44 the mobile station performs atransmission according to the transmission format (rate, duration, etc.)set in the schedule grant message. However, the mobile station continuesto maintain a rate limit that is the previously transmitted rate controlrate (PTRR) in step S45. The PTRR is defined as the actual data rate ofthe mobile station's previous transmission on the R-PDCH while actingupon the rate control instruction (e.g., RAB). When the mobile transmitson the R-PDCH while acting upon the explicit scheduling grant messageor, as described later, upon the re-transmission command (i.e., NACKsignal sent by the base station), the PTRR is not changed.

If in step S42 the mobile station does not determine that a schedulegrant message is intended for itself, then in step S46, the mobilestation determines whether an acknowledgement for a prior transmissionis expected. If so, then in step S48, the mobile station determines ifan ACK or NAK is received. If a NACK is received, then as describedabove, the mobile station retransmits based on the schedule grant forthe NACKed transmission in step S50. Particularly, the rate from thescheduled grant message is used for the retransmission. However, themobile station does maintain the rate limit that is the PTRR in stepS45.

If an ACK is received in step S48 or no acknowledgement is expected instep S46, then in step S52 the mobile station monitors the RAB. If RABare sent during the scheduling interval, then the mobile stationdetermines the transmission rate limit from the RAB and the PTRR in anywell known manner, and transmits data on the R-PDCH using a rate that isequal to or less than the rate limit if the mobile station's buffer isnot empty. The PTRR is then updated to the actual transmission rate. If,in step S52, the mobile station does not detect RAB on the F-UCACH, thenprocessing proceeds to step S45. After steps S45 and S54, processingproceeds to step S40.

As described above, if a schedule grant message is received, the rate inthe schedule grant message overrides the rate limit from the receivedRAB bits meanwhile the PTRR is not updated. And, for subsequent frames,if no further scheduling grant messages are received, the rate limit isdetermined from the received RAB bits and the PTRR then the PTRR isupdated, except if a retransmission of a previously scheduledtransmission is required.

Next, the operational process at the base station will be described withrespect to FIGS. 5A-5B. As shown, the base station, in any well knownmanner (e.g., based on the previous decoding results), determines theset of mobile stations that require a new transmission excluding mobilestations with pending retransmission during the frame in step S60. Thenin step S62, the base station determines the supportable rate for eachmobile station in the set based on the channel conditions, transmitpower headroom, data in the buffer of each mobile station, etc. Becausestep S62, like step S60, is so well known, this step will not bedescribed in detail.

Subsequently, in step S64, the base station prioritizes the mobilestations for scheduling. In one embodiment of the present invention, theprioritizing is performed based on the rate difference between thesupportable rate determined in step S62 and the current rate limit setforth by the RAB. Specifically, the base station ranks the mobilestations having the greatest rate difference from highest priority tolowest priority, and places the ranked mobile stations having a ratedifference greater than a predetermined threshold on a scheduling list.

Next, in step S66, the base station determines which mobile stations onthe scheduling list to schedule according to the scheduled transmissionmethod and which mobile stations to schedule according to the commonrate control scheduling method. Furthermore, in step S66, the basestation determines the rate among other things (e.g., transmissionformat) for the mobile stations being scheduled according to thescheduled transmission method. FIG. 5B illustrates a flow chart showingthe process steps performed by the base station in performing step S66.

As shown in FIG. 5B, the base station starts with the highest prioritymobile station on the scheduling list as the mobile station underconsideration; hereinafter, the considered mobile station. Then, in stepS80, the base station determines if the available load is less thanzero. In general, load is the accumulated signal power of each mobilestation's transmission. However, a base station has a maximum load thatit can support. The available load is the maximum supportable load minusa currently expected load from mobile station transmissions. At thebeginning of the scheduling procedure, the available load is determinedas the maximum load minus the combination of

-   -   the load that retransmissions of data packets would cause; and    -   the sum of PTFRR_DOWN_rate loads of the mobile stations in the        set (see step S60) of mobile stations.

PTRR_DOWN_rate load is defined as the load contribution of a newtransmission if the transmission were made in response to RAB of DOWNsent by the base station and the mobile station made the newtransmission by acting upon this DOWN command probabilistically withrespect to its PTRR. More specifically, as is well known with respect tocommon rate control according to HRPD,PTRR_DOWN_rate load=(the probability that mobile transmits at (PTRR downby one step rate) times the load of (PTRR down by one step rate))+(theprobability that mobile transmits at PTRR rate times the load of PTRRrate)Similarly,PTRR_UP_rate load=(the probability that mobile transmits at (PTRR up byone step rate) times the load of (PTRR up by one step rate))+(theprobability that mobile transmits at PTRR rate times the load of PTRRrate)It will further be appreciated, as is well known with respect to commonrate control according to HRPD, the rate transition probabilities foreach PTRR can be different and are known at both the base station andthe mobile station

If in step S80, the base station determines that the available load isnot less than zero, then in step S82, the base station determines if theavailable load plus the PTRR_DOWN_rate load of the considered mobilestation is greater than the load if the considered mobile station made atransmission at its supportable rate (which was determined in step S62).

If the determination in step S82 is positive, then in step S84, the basestation schedules the considered mobile station for transmissionaccording to the scheduled transmission method and at the consideredmobile station's supportable rate. Next, in step S86, the base stationupdates the available load by (i) adding the PTRR_DOWN_rate load of theconsidered mobile station and (ii) subtracting the load if theconsidered mobile station made a transmission at its supportable rate.

Then in step S88, the base station determines if the any other mobilestations remain on the scheduling list. If so, then in step S90, thenext mobile station in terms of priority on the scheduling list becomesthe considered mobile station, and processing returns to step S80.

Returning to step S82, if the determination in this step is negative,then processing proceeds directly to step S88. An alternative at thisstep is to determine a lower supportable rate for the mobile that wouldsatisfy the test of step S82. If such a rate exists and is substantiallydifferent from the mobile's current rate limit, then step S84 isentered. If not, step S88 is entered. In step S88, if the schedulinglist has been exhausted, then processing proceeds to step S92. Also, ifin step S80, the base station determines that the available load is lessthen zero, then processing proceeds to step S92.

In step S92, the base station treats the unscheduled mobile stations onthe scheduling list as rate controlled mobiles. Namely, these mobilestations will be scheduled according to the common rate controlscheduling method, as will the mobile stations that did not make thescheduled list but formed part of the set of mobile stations determinedin step S60.

Returning to FIG. 5A, after step S66, the base station determines instep S68 if (i) the available load resulting from step S66 plus (ii) thesum of the PTRR_DOWN_rate loads of the rate controlled mobile stationsis greater than the sum of the PTRR_UP_rate loads of the rate controlledmobile stations. If so, then in step S70, the base station schedules therate controlled mobiles according to the common rate control schedulingmethod by sending RAB set to UP. If the determination in step S68 isnegative, then in step S72, the base station schedules the ratecontrolled mobile stations according to the common rate controlscheduling method by sending RAB set to DOWN. In an alternative approachto steps S68-S72 where the RAB is a three-state (Up, Hold, and Down)indication, two thresholds are tested. Here, if the available load plusthe sum of loads of all rate-controlled mobiles' PTRR_Down_rates isgreater than the sum of loads of all rate-controlled mobiles'PFRR_Up_rates, RAB is set to Up; else if the available load plus the sumof loads of all rate-controlled mobiles'PTRR_Down_rates is greater thanthe sum of loads of all rate-controlled mobiles' PTRRs, the RAB is setto Hold; else the RAB is set to Down. Other rate control alternatives,such as those described previously in this disclosure, may also be usedin place of steps S68-S72.

As will be appreciated, in the second embodiment, the available loaddetermines the assigned rates. Namely, scheduling of individual mobilestations is possible in conjunction with common rate control scheduling.After an individual rate is assigned to each scheduled mobile station,the available load is recalculated by subtracting the additional loadthat is due to the newly scheduled transmission. Rate-controlled mobilestations are then defined as those mobile stations that are notscheduled or are not re-transmitting.

In the second embodiment, an alternative method for the mobile todetermine the power level on the R-SPICH can be based on the powerlevels for the rates that the mobile can possibly choose to transmit andthe probabilities that the mobiles choose those rates. Morespecifically, mobile_R-SPICH_power=sum of (R-SPICH power if rate i istransmitted times the probability that the mobile chooses rate i totransmit) over i, for i is any rate that the mobile can choose totransmit in response to the RAB and the PTRR. Since the transitionprobabilities are known to both the base station and mobile station,there is no ambiguity regarding what power level to be used on theR-SPICH. After the mobile selects a particular rate j, the mobile willapply an adjustment to the traffic-to-pilot ratio on the packet datachannel to ensure the power level of the packet data channel is correctfor the fmal selected rate j (i.e. to correct any deficits if theR-SPICH power of rate j is higher than the MS_R-SPICH_power or anysurpluses if the R-SPICH power of rate j is lower than theMS_R-SPICH_power).

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications are intended to be included within the scope of thefollowing claims.

1. A method of controlling reverse link transmission by at least onemobile station, comprising: first scheduling a reverse link transmissionby at least one mobile station by sending a schedule grant messageaccording to a first scheduling protocol, the schedule grant messageproviding the at least one mobile station with approval to transmit, theschedule grant message further establishing a rate limit fortransmissions scheduled according to a second scheduling protocol. 2.The method of claim 1, wherein the first scheduling protocol is ascheduling mode protocol and the second scheduling protocol is a ratecontrol mode protocol.
 3. The method of claim 1, further comprising:second scheduling a subsequent reverse link transmission by the mobilestation by sending a rate control instruction according to the secondscheduling protocol.
 4. The method of claim 3, wherein the firstscheduling step sends the schedule grant message over a first forwardcontrol channel and the second scheduling step sends the rate controlinstruction over a second forward control channel.
 5. The method ofclaim 3, wherein the rate control instruction indicates to transmit atthe rate limit.
 6. The method of claim 5, wherein a failure to send arate control instruction indicates not to transmit.
 7. The method ofclaim 3, wherein the rate control instruction indicates one of anincrease and a decrease in the rate limit.
 8. The method of claim 3,further comprising: sending another schedule grant message that resetsthe rate limit.
 9. The method of claim 3, further comprising:determining a change in rate limit between a previously scheduledtransmission and a currently scheduled transmission; and performing thesecond scheduling step when the determined change does not exceed athreshold amount.
 10. The method of claim 1, further comprising: sendinganother schedule grant message that resets the rate limit.
 11. A methodof controlling reverse link transmission by at least one mobile station,comprising: scheduling a reverse link transmission by at least onemobile station by sending a schedule grant message according to a firstscheduling protocol, the schedule grant message providing the at leastone mobile station with approval to transmit, the schedule grant messageresetting a rate limit for transmissions scheduled according to a secondscheduling protocol.
 12. The method of claim 11, wherein the firstscheduling protocol is a scheduling mode protocol and the secondscheduling protocol is a rate control mode protocol.
 13. A method ofmaking reverse link transmission, comprising: transmitting based on arate limit set by a previously received schedule grant message if a ratecontrol instruction is received.
 14. The method of claim 13, wherein thepreviously received schedule grant message is received over a firstchannel and the rate control instruction is received over a secondchannel.
 15. The method of claim 13, further comprising: reducing therate limit if no rate control instruction is received; and increasingthe rate limit if a rate control instruction is received.
 16. The methodof claim 13, further comprising: adjusting the rate limit based on anaccumulation of rate control instructions received since the previouslyreceived schedule grant message.
 17. A method of making reverse linktransmission, comprising: transmitting based on a rate of a previoustransmission made in response to a previously received schedule grantmessage if a rate control instruction is received.
 18. A method ofcontrolling reverse link transmission by at least one mobile station,comprising: overriding a common rate control instruction for the atleast one mobile station by sending a schedule grant message for the atleast one mobile station.
 19. The method of claim 18, furthercomprising: first determining whether to override a common rate controlinstruction for a mobile station based on an available load at a basestation; and performing the overriding step for a mobile station whenthe determining step determines to override the common rate controlinstruction for the mobile station.
 20. The method of claim 19, whereinthe determining step determines whether to override the common ratecontrol instruction for the mobile station based on the available loadat the base station, an estimated increase in the available load if themobile station ignores the common rate control instruction and anestimated reduction in the available load if the mobile stationtransmits in response to a schedule grant message.
 21. The method ofclaim 19, further comprising: second determining, for each mobilestation in a set of mobile stations to be scheduled, whether to considerthe mobile station for overriding the common rate control instructionbased on a rate supported by the mobile station and a rate limit setforth according to a previous common rate control instruction; andperforming the first determining step with respect to the mobilestations determined in the second determining step.
 22. A method ofcontrolling reverse link transmission by at least one mobile station,comprising: first transmitting, at a mobile station, according to aschedule grant message instead of a common rate control instruction. 23.The method of claim 22, wherein the transmitting step is aretransmission of a negative-acknowledged transmission sent in responseto a schedule grant message.
 24. The method of claim 22, furthercomprising: second transmitting, subsequent to the first transmitting,according a common rate control instruction and a rate of transmissionin response to a previous common rate control instruction.
 25. Themethod of claim 22, further comprising: setting a secondary pilot levelbased on a weighted average of the secondary pilot levels correspondingto possible transmission rates.
 26. A method, comprising: transmitting apilot signal on the reverse link at a power derived from a rate assignedto the mobile station for a scheduled transmission.